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A076389 Sum of squares of numbers that cannot be written as t*n + u*(n+1) for nonnegative integers t,u.

%I A076389 #5 Jul 05 2025 08:47:28
%S A076389 0,1,30,220,950,3045,8036,18480,38340,73425,131890,224796,366730,
%T A076389 576485,877800,1300160,1879656,2659905,3693030,5040700,6775230,
%U A076389 8980741,11754380,15207600,19467500,24678225,31002426,38622780,47743570
%N A076389 Sum of squares of numbers that cannot be written as t*n + u*(n+1) for nonnegative integers t,u.
%D A076389 Fred. Schuh, Vragen betreffende een onbepaalde vergelijking, Nieuw Tijdschrift voor Wiskunde, 52 (1964-1965) 193-198.
%H A076389 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-21,35,-35,21,-7,1).
%F A076389 n^2*(n^2-1)*(n^2-n-1)/12.
%F A076389 G.f.:(1+23*x+31*x^2+5*x^3)*x^2/(1-x)^7
%p A076389 seq(n^2*(n^2-1)*(n^2-n-1)/12,n=1..40);
%Y A076389 Cf. A002417, A076460-A076465.
%K A076389 easy,nonn
%O A076389 1,3
%A A076389 _Floor van Lamoen_, Oct 09 2002